GB2281101A

GB2281101A - I.c.engine fuel vaporiser

Info

Publication number: GB2281101A
Application number: GB9314897A
Authority: GB
Inventors: Michael David Fry
Original assignee: University College London
Current assignee: University College London
Priority date: 1993-07-19
Filing date: 1993-07-19
Publication date: 1995-02-22
Anticipated expiration: 2013-07-19
Also published as: GB9314897D0; GB2281101B

Abstract

A fuel injector 15 supplies liquid fuel into a chamber 12 containing a glow plug 18 and having an air inlet 14. Under cold start/warm up engine conditions the plug 18 is switched on and causes the liquid fuel to become vaporised before leaving the chamber 12 through the nozzle 20 and entering the engine inlet port. The air supply to the inlet 14 may be at atmospheric pressure or supplied under pressure and filtered exhaust gas may be supplied to the inlet. The chamber walls may have passages for exhaust gases to provide heating and the nozzle 20 may contain a one-way poppet valve. <IMAGE>

Description

COMBINED FUEL VAPORISER AND ATOMISER This invention relates to a combined fuel vaporiser and air-assisted atomiser, intended for use on a spark ignition (SI) engine. The device is intended to reduce the emissions of carbon monoxide (CO) and unburnt hydrocarbons (HCs) from such an engine by first heating the fuel to aid vaporisation during the engine's cold start/warm-up phase, and subsequently atomising the liquid fuel to improve the performance of the fully warm engine.

Hydrocarbon fuels will only burn when in their gaseous form. In order for the fuel to be burnt efficiently the fuel should ideally be fully vaporised and mixed with air at the time of ignition. Current gasoline injection systems inject fuel in its liquid form into the engine inlet port, usually while the inlet valves are closed. This fuel impacts on the metal surfaces and begins to evaporate. The time delay between injection and ignition in a port injection engine will be less than 120ms, even at idle conditions. Thus, the time scale for the evaporation process is very short. While the engine is cold only the lighter fractions of gasoline will evaporate and so only a proportion of the fuel is in a combustible state at the time of ignition; additional fuel must be added during this period if reliable combustion is to occur.

During this initial running period, not only are the HC emissions of the base engine very high, but also the exhaust catalyst will be highly inefficient as it takes up to two minutes to reach its operating temperature.

As a consequence, up to 80% of the HC and CO emissions produced in a US emissions test are emitted during the first 2 to 3 minutes after cold start.

Any measures that reduce the need for cold start fuel enrichment will therefore have a significant effect upon the ability of an engine to pass the homologation emissions test. Heating the fuel so that it is fully vaporised has been shown to reduce substantially or even eliminate the cold start enrichment requirement.

For a fuel heating device to be practicable it must require a minimal electrical power input. This can be achieved by turning off the electrical power to the heating apparatus once the exhaust catalyst has attained its working temperature. However, at this stage the fuel preparation must still be good to minimise unburnt HC emissions, particularly during transients. Some strategies for producing low emissions rely on diluting the charge with excess air ("lean burn") or with recirculated exhaust gas (egr) or a combination of the two. Under these circumstances it may be advantageous to employ the fuel heater at other times besides the start and warming phase.

In an existing device developed by National Engineering Laboratory (NEL), a length of tubing, for example made of brass, with a heating element coiled about its exterior surface is placed between the outlet of the fuel injector and the engine inlet port. During the cold start/warm-up phase the heating element is switched on and the injector sends a narrow jet of fuel into the tube. The fuel is diverted by a radial jet of air to hit the walls of the tube. A further pair of air jets with tangential components add swirl to the fuel stream so that it spirals around the walls of the tube, becomes heated by the heating element and vaporises before entering the engine inlet port.

However, there are a number of problems with this device. Firstly, in order to incorporate the tube the fuel injector must be positioned further away from the engine inlet port than usual, thus creating a need to redesign certain parts of the engine. The extra distance that the fuel must travel down the tube also increases the transport time between the fuel leaving the injector and entering the engine inlet port.

Secondly, when the engine is fully warm and the heating element is switched off, the diverting air jets are no longer provided. Therefore, the fuel remains as a narrow liquid jet and only the usual system of vaporisation once the fuel impacts the metal surfaces is relied upon to produce a gaseous fuel mixture.

In order to avoid these problems, the present invention provides a compact mixture preparation device capable of supplying either fuel vapour or finely atomised liquid fuel spray into the engine inlet port.

The device combines a small heated chamber with an air assisted atomiser so that a substantially improved mixture preparation is achieved both under cold conditions (heated mode) and under fully warm conditions (air assisted mode). The device is designed to be compact so that it can be substituted for a conventional fuel injector and fitted into a current engine without modification to the fuel rail or to the manifold. A conventional fuel injector can be used to meter the fuel into the heated chamber.

Accordingly, the present invention provides a fuel injection system for a spark ignition engine comprising a chamber for connection to an engine induction system, a fuel injector connected to the chamber to deliver a charge of fuel, an air supply inlet to the chamber to allow air to be supplied to the chamber, a heater for vaporising fuel received in the chamber from the injector and at least one outlet orifice from the chamber to the induction system to deliver a vaporised jet of fuel through the at least one outlet orifice to the engine induction system for combustion.

Preferably, the heater comprises a glow plug. The heater may also extend into one end of a cylindrical chamber, very closely spaced from the walls thereof.

The outlet orifice is preferably located at the other end of the chamber and may be tapered.

Preferably, an outlet from the fuel injector opens into a fuel entry passageway which opens into the chamber at an inclined angle to the longitudinal axis of the chamber.

The air supply inlet preferably comprises a further passageway which opens into the fuel entry passageway at an inclined angle thereto.

The invention will now be described in detail, by way of example only, with reference to the accompanying drawing, Figure 1, which shows a sectional view of the fuel injection device.

The fuel injection system indicated generally at 10 comprises a first housing 11 which defines a substantially cylindrical chamber 12, a fuel entry passageway 13 and an air supply inlet 14. The fuel entry passageway 13 opens into the chamber 12 and is inclined at an angle to the longitudinal axis of the chamber 12. The air supply inlet 14 opens into the fuel entry passageway 13 and is inclined at an angle thereto.

A conventional fuel injector 15 is located in a second housing 16 adjacent the first housing 11. The first 11 and second 16 housings may be thermally isolated from one another. The outlet 17 of the fuel injector 15 protrudes from the second housing 16 and into the fuel entry passageway 13 so that the fuel injector 15 can supply a charge of fuel into chamber 11 through the fuel entry passageway 13.

A heater 18 extends into one end of the cylindrical chamber 12 and is very closely spaced from the walls of the chamber 12. The heater 18 may be in the form of a conventional glow plug, capable of reaching very high temperatures within a few seconds of being switched on.

A plug 19 is sealingly fitted into the other end of chamber 12. The plug 19 has at least one orifice 20 therethrough to provide an outlet from the chamber 12 to the engine inlet port (not shown). The orifice has a significantly smaller cross-section than that of the chamber. The orifice 20 may be tapered and may diverge in a direction from the chamber towards the engine inlet port to form a nozzle. The orifice 20 may optionally be fitted with one way poppet valve (not shown).

The operation of the device is as follows. In use in the cold start/warm-up phase, the heater 18 is switched on. The injector 15 supplies a jet of liquid fuel into the chamber 12, and this fuel is vaporised by the heat. The fuel vapour mixes with the air stream entering through air supply inlet 14 and passes through nozzle 20 into the engine inlet port.

When the engine is fully warm, the heater 18 is switched off. As before, the injector 15 supplies liquid fuel into the chamber 12. This mixes with the air stream entering through air supply inlet 14 and the mixture passes through nozzle 20. The pressure difference across the nozzle 20 causes the fuel to atomise into a fine spray, thus producing a suitable gaseous mixture for combustion.

As described earlier in the specification, in order to maintain low engine emissions it may be advantageous to switch on the heater at other times besides the cold start/warm up phase to vaporise the fuel and ensure optimum mixture preparation.

Therefore, the invention is not limited to the use of the heater only during cold start/warm up. In addition, the first housing 11 may have one or more passages running through it, through which a proportion of the engine exhaust gases may be circulated in order to heat up the housing and obtain some further vaporisation of the fuel without the use of the heater 18.

The air stream entering through inlet 14 may be air at atmospheric pressure which bleeds through the inlet due to the lower pressure in the engine inlet manifold. Alternatively, means may be provided to supply air under pressure or to filter and supply a proportion of the engine exhaust gases. Furthermore, means may be provided to modulate the flow of air or exhaust gas entering chamber 12 through air supply inlet 14 in order to optimise the supply of air to the engine for particular engine operating conditions.

The device is sufficiently compact that it may be substituted for a normal fuel injector in a standard engine and does not necessitate any modification to the fuel rail or manifold.

Thus, the device can produce either a fuel vapor or an atomised fuel spray to provide a combustible mixture and its use results in reduced engine emissions both during the cold start/warm-up and fully warm engine conditions.

Claims

1. A fuel injection system for a spark ignition engine comprising a chamber for connection to an engine induction system, a fuel injector connected to the chamber to deliver a charge of fuel, an air supply inlet to the chamber to allow air to be supplied to the chamber, a heater for vaporising fuel received in the chamber from the injector and at least one outlet orifice from the chamber to the induction system to deliver a vaporised jet of fuel through the outlet to the engine induction system for combustion.

2. A fuel injection system as claimed in claim 1 wherein the heater comprises a glow plug.

3. A fuel injection system as claimed in claim 1 or claim 2 wherein the chamber is cylindrical and the heater extends into one end thereof, the heater being very closely spaced from the walls of the chamber, and the at least one outlet orifice is located at the other end of the cylindrical chamber.

4. A fuel injection system as claimed in any preceding claim wherein the outlet orifice is tapered and diverges in a direction from the chamber towards the engine induction system.

5. A fuel injection system as claimed in claim 4 wherein the tapered orifice has a one-way poppet valve located therein.

6. A fuel injection system as claimed in any preceding claim wherein an outlet from the fuel injector opens into a fuel entry passageway which opens into the chamber at an inclined angle to the longitudinal axis of the chamber.

7. A fuel injection system as claimed in claim 6 wherein the air supply inlet comprises a further passageway which opens into the fuel entry passageway at an inclined angle thereto.

8. A fuel injection system as claimed in any preceding claim wherein the air supply inlet comprises an inlet for ambient air.

9. A fuel injection system as claimed in any of claims 1 to 7 wherein the system further comprises means to supply air at a given pressure into the chamber through the air supply inlet.

10. A fuel injection as claimed in any of claims 1 to 7 wherein the system further comprises means to filter and supply a proportion of the engine exhaust gases into the chamber through the air supply inlet.

11. A fuel injection system as claimed in any preceding claim wherein means are provided to modulate the flow of air through the air supply inlet.

12. A fuel injection system as claimed in any preceding claim wherein the fuel injector is thermally isolated from the chamber.

13. A fuel injection system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.